Error Of Fatty Acid Oxidation Research Articles

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials.

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Results of clinical trials of a specialized product for enteral nutrition: Nutrigen Low Fat

BACKGROUND: Hereditary disorders of fatty acid oxidation are a group of fermentopathies caused by biallelic mutations in genes encoding enzymes of the mitochondrial -oxidation cascade of fatty acids. Mitochondrial fatty acid oxidation deficiency is a genetically heterogeneous group of diseases in humans caused by defects in mitochondrial fatty acid -oxidation. A common characteristic of all mitochondrial fatty acid -oxidation disorders is hypoketotic hypoglycemia, resulting from an increased dependence on glucose oxidation and an inability to synthesize ketone bodies from fatty acids. The clinical manifestations of diseases in this group are highly variable. Patients with a defect in the oxidation of long-chain fatty acids are at risk of developing cardiac and skeletal muscle abnormalities, including cardiomyopathy and arrhythmias, which can progress to early death, as well as rhabdomyolysis and exercise intolerance. The optimal composition of Nutrigen Low Fat enteral mixture allows its use in children with intestinal dysfunction and metabolic disorders as a component of nutritional support or the sole source of nutrition.
 AIMS: To study the clinical evidence on intestinal insufficiency syndrome in critically ill children, to assess the role of enteral nutrition in intestinal dysfunction prevention and treatment in critically ill patients in the pediatric intensive care unit, and to perform clinical monitoring of young children with inborn errors of fatty acid oxidation.
 MATERIALS AND METHODS: Twelve children aged 3 months to 7 years with digestive dysfunction took part in the study. The study duration was 3 weeks. During the intervention, children received the product Nutrigen Low Fat in accordance with their age and individual nutritional needs. Throughout the study, the childrens nutritional status and the dynamics of digestive dysfunction were taken into account. A clinical trial of the dry complete enteral product Nutrigen Low Fat took place from May to August of 2021. A clinical trial of the product was conducted against a background of generally accepted medical treatment in accordance with the character of the disease. The study design was an observational, longitudinal cohort study.
 RESULTS: The dynamics of objective clinical and laboratory data, as well as subjective patient characteristics, indicated an improvement in well-being, physical development, and positive dynamics of blood parameters. The product Nutrigen Low Fat meets the hygienic requirements for the composition and quality of pediatric medical nutrition products and has good organoleptic characteristics. It should be noted that Nutrigen Low Fat is convenient to use because it allows individual selection of the dilution and dosage in accordance with the childs age and clinical status, has a high biological value (contains easily absorbed fat, with 84% medium-chain triglycerides, and easily digestible milk protein comprised of 60% whey). The products gluten-free formula is another advantage.
 CONCLUSIONS: All of the above allows us to recommend the use of a complete product, Nutrigen Low Fat, as a supplement to the diet or as the sole source of nutrition. It can be used for oral nutrition (sipping) or tube feeding from birth in children with acute surgical and therapeutic diseases, as well as orphan inborn errors, including fatty acid oxidation errors, with maldigestion and malabsorption syndrome, intoxication, and malnutrition.

Diabetes Mellitus Type 1 in Patient with Medium-Chain Acyl-Coenzyme A Dehydrogenase Deficiency

Introduction: Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) is an inborn error of fatty acid oxidation requiring carbohydrate (CHO) to avoid disabling encephalopathy with non-ketotic hypoglycemia. We report diagnosis and management of T1DM in an MCADD patient. Case Presentation: Our patient was born prior to MCADD newborn screening. She did well until 2 months of age when she slept 12 hours without feeding and BG 20 mg/dl in ER required IV glucose. By 1 1/2 y/o she had 3 similar events. Pediatric endocrine identified MCADD. She avoided severe hypoglycemia by attending to CHO intake especially during illness. At 8 y/o, she noted glucosuria without ketonuria. Her test results were normal with hemoglobin A1c (HgbA1c) 5.3%. She responded well to adjusted CHO diet until 13 y/o when she noted lethargy with persistent high BG. T1DM was diagnosed with her HgbA1c 6.7%. We hypothesized long-acting glargine insulin could assist BG control without hypoglycemia. She responded well to insulin to maintain HgbA1c less than 7.5% until 15 years of age when she expressed compliance problems to present. Results: Her MCADD presented with non-ketotic hypoglycemia events, normal plasma carnitine but elevated MCADD specific octanoyl-acyl-carnitine levels. A known MCADD mutation was identified. At 13 y/o her BG 335 mg/dl, abnormal insulin release and positive pancreas islet directed antibodies were consistent with T1DM. After 1 year glargine therapy alone she required additional insulin to maintain excellent T1DM control. Discussion: MCADD requires early detection to reduce risk for tragic mortality and morbidity. Our patient requires CHO favored diet but is not obese as sometimes reported with MCADD. Management of her T1DM with MCADD requires insulin monitored to avoid hypoglycemia. T1DM is rarely or not reported in patients with MCADD. Conclusion: BG control in MCADD patients must focus on avoiding hypoglycemia but consider T1DM or other DM when an MCADD patient has persistent hyperglycemia. Disclosure G.W. Moll: None.

Recurrent ACADVL molecular findings in individuals with a positive newborn screen for very long chain acyl-coA dehydrogenase (VLCAD) deficiency in the United States.

Very long chain acyl-coA dehydrogenase deficiency (VLCADD) is an autosomal recessive inborn error of fatty acid oxidation detected by newborn screening (NBS). Follow-up molecular analyses are often required to clarify VLCADD-suggestive NBS results, but to date the outcome of these studies are not well described for the general screen-positive population. In the following study, we report the molecular findings for 693 unrelated patients that sequentially received Sanger sequence analysis of ACADVL as a result of a positive NBS for VLCADD. Highlighting the variable molecular underpinnings of this disorder, we identified 94 different pathogenic ACADVL variants (40 novel), as well as 134 variants of unknown clinical significance (VUSs). Evidence for the pathogenicity of a subset of recurrent VUSs was provided using multiple in silico analyses. Surprisingly, the most frequent finding in our cohort was carrier status, 57% all individuals had a single pathogenic variant or VUS. This result was further supported by follow-up array and/or acylcarnitine analysis that failed to provide evidence of a second pathogenic allele. Notably, exon-targeted array analysis of 131 individuals screen positive for VLCADD failed to identify copy number changes in ACADVL thus suggesting this test has a low yield in the setting of NBS follow-up. While no genotype was common, the c.848T>C (p.V283A) pathogenic variant was clearly the most frequent; at least one copy was found in ~10% of all individuals with a positive NBS. Clinical and biochemical data for seven unrelated patients homozygous for the p.V283A allele suggests that it results in a mild phenotype that responds well to standard treatment, but hypoglycemia can occur. Collectively, our data illustrate the molecular heterogeneity of VLCADD and provide novel insight into the outcomes of NBS for this disorder.

Propofol-related infusion syndrome heralding a mitochondrial disease: Case report

Propofol-related infusion syndrome (PRIS) is a rare but catastrophic complication of propofol use. It is clinically characterized by metabolic acidosis, rhabdomyolysis, arrhythmias, myocardial failure, renal failure, and hepatomegaly, and may lead to death.1 Some risk factors are associated with PRIS, namely young age, critical illness, high fat intake, catecholamine or steroid use, inborn error of fatty acid oxidation, propofol doses exceeding 4–5 mg/kg/hour, and duration of use exceeding 48 hours.1 Some evidence also suggests that PRIS is related to a mitochondrial toxicity of propofol.2,3 The authors thank Éric Laflamme for his help revising this manuscript.

Sudden unexpected infant death (SUDI) in a newborn due to medium chain acyl CoA dehydrogenase (MCAD) deficiency with an unusual severe genotype

Medium chain acyl CoA dehydrogenase deficiency (MCAD) is the most common inborn error of fatty acid oxidation. This condition may lead to cellular energy shortage and cause severe clinical events such as hypoketotic hypoglycemia, Reye syndrome and sudden death. MCAD deficiency usually presents around three to six months of life, following catabolic stress as intercurrent infections or prolonged fasting, whilst neonatal-onset of the disease is quite rare. We report the case of an apparently healthy newborn who suddenly died at the third day of life, in which the diagnosis of MCAD deficiency was possible through peri-mortem blood-spot acylcarnitine analysis that showed very high concentrations of octanoylcarnitine. Genetic analysis at the ACADM locus confirmed the biochemical findings by demonstrating the presence in homozygosity of the frame-shift c.244dup1 (p.Trp82LeufsX23) mutation, a severe genotype that may explain the unusual and very early fatal outcome in this newborn. This report confirms that inborn errors of fatty acid oxidation represent one of the genetic causes of sudden unexpected deaths in infancy (SUDI) and underlines the importance to include systematically specific metabolic screening in any neonatal unexpected death.

Macro-AST: misleading finding in an adolescent with MCAD-deficiency

BackgroundMCAD-deficiency is the most common inborn error of fatty acid oxidation now included in many newborn screening programms using MS/MS. During prolonged catabolic episodes, patients may suffer from metabolic decompensation with dysfunction of liver, skeletal- and heart muscle as well as brain. In anabolism, neither clinical symptoms nor biochemical signs of organ dysfunction occur.Case presentationWe report a female patient with MCAD-deficiency in whom at the age of 11 years isolated AST-elevation was found without any clinical or biochemical signs of organ dysfunction. We showed by polyethylene glycol precipitation that macro-AST formation was responsible for this biochemical finding. AST was probably complexed with immunoglobulins possibly related to an allergic disposition. Macro-AST formation is not a special feature of MCAD-deficiency but rather a non-specific, coincidental finding which also occurs in healthy individuals. The general practitioner consulted by the patient before coming to our outpatient clinic for inborn errors of metabolism was worried that isolated AST-elevation indicated cell damage in MCAD-deficiency. He ordered further diagnostic tests like ultrasound, ECG and echocardiography without any pathology.ConclusionIn isolated AST-elevation, macro-AST has to be considered in order to avoid unnecessary, costly and invasive evaluation. This is not only true for healthy persons but for patients with chronic diseases like MCAD as well.

Newborn screening for medium chain acyl CoA dehydrogenase deficiency

Medium chain acyl CoA dehydrogenase deficiency (MCADD) is an uncommon inborn error of fatty acid oxidation that is a preventable cause of morbidity and mortality. Newborn screening for MCADD has...

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency and cardiogenic shock

Mitochondrial fatty acids beta-oxidation provides the major source of energy for heart, liver and skeletal muscle. Several enzymes are involved in this spiral cycle. Long chain 3 hydroxyacil CoA dehydrogenase (LCHAD) deficiency is a rare, autosomal recessive inborn error of fatty acid oxidation. Clinical presentation usually is hypoketotic hypoglycemia but other sings and symptoms such as failure to thrive, feeding difficulties, cholestatic, hepatic dysfunction, peripheral neuropathy, pigmentary retinopathy, hypotonia, recurrent muscular pains, cardiomyopathy (dilated or hypertrophic), arrhytmias or sudden death can be found [1–4].

Carnitine Membrane Transporter Deficiency: A Rare Treatable Cause of Cardiomyopathy and Anemia

Carnitine transporter defect is an autosomal recessive disorder caused by mutations in the SLC22A5 gene that encodes the high-affinity carnitine transporter OCTN2. Affected patients can present with predominant metabolic or cardiac manifestations. Early recognition of this disorder in a context of life-threatening cardiac failure and treatment with carnitine can be lifesaving in this inborn error of fatty acid oxidation. Here we describe a boy with a severe cardiomyopathy and severe anemia who improved with carnitine therapy. Physiopathology of anemia, a probably less recognized symptom of carnitine deficiency, is also discussed.

Prolonged moderate‐intensity exercise without and with L ‐carnitine supplementation in patients with MCAD deficiency

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is probably the most common inborn error of fatty acid oxidation (FAO). Routine L-carnitine supplementation in the treatment of MCADD is controversial. To establish the effects of L-carnitine supplementation during prolonged moderate-intensity exercise in MCADD, five patients and three control subjects were studied during 2 hours of moderate-intensity exercise after a 12-hour fast. Patients were studied twice, once with and once without L-carnitine supplementation (50 mg/kg per day). Blood samples were collected before, during and after exercise, and analysed for routine parameters, acylcarnitines and carnitine biosynthesis intermediates. Urine was collected before and after exercise, and analysed for acylcarnitines. All patients were able to complete the exercise test without any apparent clinical or biochemical adverse effects, even without L-carnitine supplementation. A significant rise in plasma free fatty acids and octanoylcarnitine levels during exercise was seen in all patients, indicating a substantial increase in FAO during exercise. Octanoylcarnitine levels in plasma were significantly higher in patients with L-carnitine supplementation, suggesting increased clearance of accumulating acylcarnitines. A statistically significant increase of plasma and urinary free carnitine levels, as well as of plasma gamma-butyrobetaine was seen in MCADD patients without L-carnitine supplementation. These data suggest an increase in carnitine biosynthesis. In conclusion, although L-carnitine supplementation may promote clearance of accumulating acylcarnitines during moderate-intensity exercise, no apparent beneficial effect of this supplementation on clinical and biochemical parameters was observed in MCADD patients. Our results suggest that MCADD patients are able to increase carnitine biosynthesis during exercise to compensate for carnitine losses.

Influence of dietary fatty acid chain-length on metabolic tolerance in mouse models of inherited defects in mitochondrial fatty acid β-oxidation

Fasting-induced metabolic disease of all inherited deficiencies of the acyl-CoA dehydrogenases is characterized by hypoglycemia, hypoketonemia, and organic aciduria. Mice with these enzyme deficiencies are cold intolerant. To evaluate the potential role that dietary fatty acid chain-length has on a patient’s ability to compensate during a metabolic challenge, we fed long-chain acyl CoA dehydrogenase (LCAD) deficient and short-chain acyl CoA dehydrogenase (SCAD) deficient mice a diet rich in medium-chain triglycerides (MCT) or long-chain triglycerides (LCT). To elucidate the importance of maintaining adequate serum glucose concentrations on compensation mechanisms during metabolic challenge, we treated LCAD−/− mice with a solution of 12.5% glucose or saline prior to fasting and a cold-challenge. We found that feeding SCAD deficient mice the LCT diet from weaning increased survival from 40 to 94% during metabolic challenge of cold tolerance. In contrast, there was no benefit to feeding the MCT diet at weaning to LCAD−/− mice; however, there was significant benefit when LCAD−/− mice were fed the MCT diet from the beginning of gestation. Survival during cold-challenge increased from 50 to 93%. In the LCAD−/− mice treated with glucose, despite maintaining serum glucose concentrations at normal or higher concentrations, the LCAD−/− mice were still unable to compensate during metabolic challenge. These results indicate the important influences dietary fatty acids may have by providing enhanced metabolic tolerance in patients with inborn errors of fatty acid oxidation. Furthermore, these studies demonstrate that there may be crucial variables involved in the treatment of these patients, including the patient’s specific enzyme deficiency, the quantity and chain-length of dietary fat, which may provide positive effects, as well as the time in development when it was administered.

Dietary Phytoestrogens Increase Metabolic Resistance (Cold Tolerance) in Long-Chain Acyl-CoA Dehydrogenase–Deficient Mice

We evaluated the role of dietary phytoestrogens (PE) in the disease phenotype of cold intolerance that characterizes long-chain acyl-CoA dehydrogenase-deficient (LCAD-/-) mice, a model of inborn errors of mitochondrial fatty acid beta-oxidation. Male LCAD-/- mice were fed a standard diet containing endogenous PE, a PE-free diet, or a PE-free diet that was supplemented with genistein (250 microg/g diet). The standard diet did not restore complete cold tolerance, but it provided more resistance (P = 0.004) to cold challenge than the PE-free diet. There was a nonsignificant difference (P < 0.07) between LCAD-/- mice fed the genistein-supplemented diet and those fed the PE-free diet. There were no differences in end-point serum glucose concentrations among the 3 groups. Serum FFA were decreased in LCAD-/- mice fed the standard diet compared with those fed the PE-free diet (P = 0.005) and the diet supplemented with genistein (P < 0.001). Serum triglyceride concentrations were greater (P < 0.05) only in LCAD-/- mice fed the genistein-supplemented diet than those fed the standard diet. These results demonstrate the beneficial effects of dietary PE on metabolic tolerance in LCAD-/- mice. Furthermore, they suggest changes that could improve pediatric formula constituents, especially with regard to management of children with inborn errors of fatty acid oxidation.

Validation of an ESI-MS/MS screening method for acylcarnitine profiling in urine specimens of neonates, children, adolescents and adults

Background: Acylcarnitine (AC) profiling in dried blood spots by means of electrospray ionisation tandem mass spectrometry (ESI-MS/MS) has proven to be a useful method in neonatal screening, able to detect inborn errors of fatty acid oxidation, amino acid, organic acid and carnitine metabolism. Furthermore, this method is becoming increasingly applied in selective screening and in prenatal and postmortal diagnostics of inborn metabolic disorders, where urine is commonly used as specimen of interest. We therefore developed and validated a butylation method of acylcarnitine profiling in urine by ESI-MS/MS without previous chromatographic separation. Methods: Random urine specimens were used for investigation of the analytical imprecision of the method. Recovery, precision and linearity were determined using methanolic standard solutions of free carnitine, octanoylcarnitine and palmitoylcarnitine at various concentrations. Results: The mean coefficients of variation of within-run and run-to-run analysis of these analytes were found between 10% and 20% and demonstrated that the method fulfills the analytical requirements within the relevant ranges of concentration. Creatinine-related and age-related reference values of free carnitine and the ACs (C2–C18) were established. The definite discrimination was possible between patients with fatty acid oxidation disorders, organic acidurias, and healthy controls. The AC profiles from patients with various specific disorders were diagnostically helpful during acute deterioration and even during conditions of well-compensated metabolic state. Conclusion: The method used in this study is suitable both for selective screening and for confirmation of diagnosis with the advantage of high-throughput quantitative measurement.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: clinical presentation and follow-up of 50 patients.

To assess the mode of presentation, biochemical abnormalities, clinical course, and effects of therapy in patients of long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. LCHAD deficiency is a rare, autosomal recessive inborn error of fatty acid oxidation. Although case reports and small series of patients have been published, these may not give a true picture of the clinical and biochemical spectrum associated with this disorder. To improve the early recognition and management of this potentially lethal disorder, we have reviewed a large cohort of LCHAD-deficient patients. A questionnaire was sent to the referring physicians of 61 unselected patients with LCHAD deficiency diagnosed in our center. The standardized questionnaire requested information about the clinical signs and symptoms at presentation, the clinical history, family history, pregnancy, biochemical parameters at presentation, treatment, and clinical outcome. Questionnaires on 50 patients (82%) were returned and included in this study. The mean age of clinical presentation was 5.8 months (range: 1 day-26 months). Seven (15%) of the patients presented in the neonatal period. Thirty-nine patients (78%) presented with hypoketotic hypoglycemia, the classical features of a fatty acid oxidation disorder. Eleven patients (22%) presented with chronic problems, consisting of failure to thrive, feeding difficulties, cholestatic liver disease, and/or hypotonia. In retrospect, most (82%) of the patients presenting with an acute metabolic derangement also suffered from a combination of chronic nonspecific symptoms before the metabolic crises. Mortality in this series was high (38%), all dying before or within 3 months after diagnosis. Morbidity in the surviving patients is also high, with recurrent metabolic crises and muscle problems despite therapy. LCHAD deficiency often presents with a combination of chronic nonspecific symptoms. Early diagnosis is difficult in the absence of the classical metabolic derangement. Survival can be improved by prompt diagnosis, but morbidity remains alarmingly high despite current therapeutic regimes.

Newborn Screening by Tandem Mass Spectrometry

After completing this article, readers should be able to: 1. List examples of disorders for which tandem mass spectrometry (MS/MS) can screen. 2. Delineate potential difficulties with MS/MS newborn screening. Tandem mass spectrometry (MS/MS) technology has shown tremendous promise in newborn screening pilot programs worldwide with its capacity to measure numerous metabolites from a dried blood spot virtually simultaneously with an extremely rapid throughput per sample (approximately 2 min). The expansion of newborn screening programs by inclusion of an additional 15 to 30 metabolic disorders has the potential to decrease significantly the morbidity and mortality associated with inborn errors of metabolism and could offer the clinician critical diagnostic information when caring for an acutely ill neonate. Newborn screening for metabolic disorders began in 1962 in the United States, with the introduction of the Guthrie bacterial inhibition assay for phenylketonuria (PKU) in a Massachusetts voluntary program. Child health advocates, including the National Association for Retarded Citizens and the March of Dimes Birth Defects Foundation, developed model legislation and lobbied for passage of newborn screening laws at the state level. As a result of these efforts, newborn screening for PKU was legally mandated in most states in the early 1960s. The success of newborn screening for PKU led to development of tests for other conditions, including metabolic disorders (eg, galactosemia, maple syrup urine disease [MSUD], homocystinuria, and biotinidase deficiency), endocrinopathies (eg, congenital hypothyroidism and congenital adrenal hyperplasia), hemoglobinopathies (eg, sickle cell disease and thalassemias), and cystic fibrosis. Different states screen for a variable number of these disorders, with most screening for three to six conditions (Figure⇓ ). Such differences reflect state political and economic environments, technologic capabilities of public health departments, regional ethnic composition, and community expectations. All states screen for PKU and congenital hypothyroidism, and 48 states screen for galactosemia. Other inborn …

Arrhythmias and conduction defects as presenting symptoms of fatty acid oxidation disorders in children.

The clinical manifestations of inherited disorders of fatty acid oxidation vary according to the enzymatic defect. They may present as isolated cardiomyopathy, sudden death, progressive skeletal myopathy, or hepatic failure. Arrhythmia is an unusual presenting symptom of fatty acid oxidation deficiencies. Over a period of 25 years, 107 patients were diagnosed with an inherited fatty acid oxidation disorder. Arrhythmia was the predominant presenting symptom in 24 cases. These 24 cases included 15 ventricular tachycardias, 4 atrial tachycardias, 4 sinus node dysfunctions with episodes of atrial tachycardia, 6 atrioventricular blocks, and 4 left bundle-branch blocks in newborn infants. Conduction disorders and atrial tachycardias were observed in patients with defects of long-chain fatty acid transport across the inner mitochondrial membrane (carnitine palmitoyl transferase type II deficiency and carnitine acylcarnitine translocase deficiency) and in patients with trifunctional protein deficiency. Ventricular tachycardias were observed in patients with any type of fatty acid oxidation deficiency. Arrhythmias were absent in patients with primary carnitine carrier, carnitine palmitoyl transferase I, and medium chain acyl coenzyme A dehydrogenase deficiencies. The accumulation of arrhythmogenic intermediary metabolites of fatty acids, such as long-chain acylcarnitines, may be responsible for arrhythmias. Inborn errors of fatty acid oxidation should be considered in unexplained sudden death or near-miss in infants and in infants with conduction defects or ventricular tachycardia. Diagnosis can be easily ascertained by an acylcarnitine profile from blood spots on filter paper.

Clinical and biochemical features of fatty acid oxidation disorders.

Inborn errors of fatty acid oxidation (FAO) represent a group of metabolic disorders that has brought forward many interesting developments, as highlighted by the rapid pace of discovery of new defects and by the recognition of an ever-increasing spectrum of clinical phenotypes. This review includes a clinical and biochemical summary of the FAO disorders known to date, a synopsis of four recently discovered defects (short-chain 3-hydroxy acyl-CoA [coenzyme A] dehydrogenase deficiency, medium-chain 3-ketoacyl-CoA thiolase deficiency, 3-hydroxy-3-methylglutaryl-CoA synthase deficiency, and long-chain fatty acid transport deficiency) and of two susceptibility variations in the short-chain acyl-CoA dehydrogenase gene, and guidelines for the biochemical work-up of candidate patients.

Analysis of carnitine esters by radio-high performance liquid chromatography in cultured skin fibroblasts from patients with mitochondrial fatty acid oxidation disorders.

Acylcarnitines are important diagnostic markers for inborn errors of fatty acid oxidation, but their analysis in body fluids may not always be reliable. Recently, disease-specific acylcarnitine profiles generated by cultured skin fibroblasts were reported to facilitate the diagnosis by localizing a specific enzymatic defect in the mitochondrial beta-oxidation pathway. Using a novel methodologic approach, fibroblasts from 16 patients with inborn errors of fatty acid oxidation and 13 control subjects were preincubated with L-[3H]carnitine to label the intracellular carnitine pool. Cells were subsequently incubated with unlabeled palmitic acid and, after methanol extraction of cells and media, labeled free carnitine and acylcarnitines were analyzed by radio-HPLC. Quantitation was based on the integrated radioactivity of individual peaks relative to the total radioactivity recovered. In control cell lines, all saturated acylcarnitines were detected, and reference values were established. With the exception of one cell line deficient in electron transfer flavoprotein, all mutant cell lines showed abnormal and disease-specific relative concentrations of acylcarnitines. Advantages of the method include use of a small number of cells, no need for trypsinization and permeabilization of cells before incubation, simple extraction without purification of the specimen before HPLC, and relatively inexpensive equipment. The method allows a focused approach to the subsequent, more laborious confirmation of a particular disease by direct enzymatic and/or molecular analysis. It remains to be established whether the method can replace widely used global measurements of fatty acid oxidation rates in vitro that do not provide specific information about the enzyme deficiency involved.

Cardiomyopathies in disorders of oxidative metabolism.

Primary cardiomyopathy is an important cause of mortality in children and adults. Apart from inherited disorders of myocardial contractile and structural proteins, several defects of energy metabolism may cause cardiomyopathy. Most of the energy required for myocardial contraction is derived from aerobic metabolism. Faulty aerobic metabolism involving the heart may be due to defects of mitochondrial oxidative phosphorylation or to defects of fatty acid oxidation. Considerable advances have been made in the last 10 years in understanding the biochemical and molecular characteristics of mitochondrial disorders. Several point mutations or large-scale re-arrangements of mitochondrial DNA have been identified in patients with cardiomyopathy, either as part of complex multisystem syndromes or as the main clinical feature. Inborn errors of fatty acid oxidation are reported with increasing frequency as a cause of metabolic dysfunction, myopathy, cardiomyopathy, and sudden death in childhood. Advances in biochemical and molecular genetic techniques have considerably improved our understanding of the metabolic disorders causing cardiomyopathy, providing new tools for classification and diagnosis of candidate patients. The present review focuses on defects of mitochondrial oxidative metabolism associated with cardiomyopathy.